Markus Böttcher North-West University Potchefstroom South Africa SALT Spectropolarimetry and Self-Consistent SED and Polarization Modeling of Blazars Markus Böttcher North-West University Potchefstroom South Africa Collaborators: Hester Schutte (NWU) Brian van Soelen, Richard J. Britto1, Johannes P. Marais (UFS) David Buckley (SAAO) 1For the Fermi-LAT Collaboration Supported by the South African Research Chairs Initiative (SARChI) of the Department of Science and Technology and the National Research Foundation of South Africa.

Multiwavelength SEDs 3C279 Disk Often ambiguity in accretion-disk (or SSC?) contribution to the optical spectrum Disk (Bottacini et al. 2016)

Synchrotron Polarization For synchrotron radiation from a power-law distribution of electrons with ne (g) ~ g-p → Fn ~ n-a with a = (p-1)/2 = fB,order 𝑝+1 𝑝+7/3 sy = fB,order 𝛼+1 𝛼+5/3 PPL p = 2 → P = fB,order * 69 % p = 3 → P = fB,order * 75 %

Compton cross section is polarization-dependent: Compton Polarization Compton cross section is polarization-dependent: e = hn/(mec2): Thomson regime: e ≈ e’ ds/dW = 0 if e∙e’ = 0 Scattering preferentially in the plane perpendicular to e. Preferred polarization direction is preserved; polarization degree reduced to ~ ½ of target-photon polarization. p e k p’ e’ k’ => PSSC ~ Psy/2

External-Compton Scattering External Compton only relevant for scattering by relativistic electrons Relativistic aberration => approx. axisymmetric rad. field in co-moving frame of e- => External-Compton emission ~ Unpolarized: e- (g) 1/g

Multiwavelength Polarization 3C279 Optical Spectropolarimetry Polarization Degree P Sy SSC Total Disk EC (Bottacini et al. 2016)

Multiwavelength Polarization 3C279 Optical Spectropolarimetry Wavelength l Polarization Degree P Sy SSC Total Disk EC (Bottacini et al. 2016)

Multiwavelength Polarization 3C279 Optical Spectropolarimetry Wavelength l Polarization Degree P Sy SSC Total Disk EC (Bottacini et al. 2016)

The Southern African Large Telescope (SALT) Johannesburg Potchefstroom (NWU) Carnarvon (MeerKAT → SKA1) Sutherland (SALT) Cape Town

The Southern African Large Telescope (SALT) 11m fixed-altitude telescope (largest single optical telescope in the southern hemisphere) Funded by international consortium (SA, USA, Germany, Poland, India, UK, New Zealand) Robert-Stobie Spectrograph (RSS): Low – medium resolution (R ~ 5000 – 9000) spectrograph with polarimetry capabilities

Spectropolarimetry Observations of Flaring Blazars SALT Large Programme: Spectroscopy / Spectropolarimetry Follow-up of High-Energy Transients (PI: D. Buckley [SAAO]) Spectropolarimetry Observations of Flaring Blazars Preliminary In the first ~ 1.5 years: ~ 15 ToO observations 8 flaring blazars (incl. IceCube-EHE-170922)

Preliminary Example: 4C +01.02 (PKS B0106+013) FSRQ at z = 2.1 Large g-ray flare in July 2016 SALT spectropol. obs. in July and Nov. 2016 Preliminary (R. J. Britto)

Preliminary 4C +01.02 (PKS B0106+013) Lya C IV 1549 (z = 2.1) Significant (and time-variable) optical polarization Decreasing towards shorter wavelength => Addition of unpolarized component (accretion disk). Preliminary (B. v. Soelen, R. J. Britto)

4C +01.02 Previous SED modeling (Ghisellini et al. 2011) Would predict unpolarized optical emission! = 14 MBH = 5x109 M0 Ld = 7.5x1046 erg/s LB/Le = 15 (Ghisellini et al. 2011)

Preliminary Preliminary 4C +01.02 Quasi-simultaneous SED + spectropolarimetry modeling: Preliminary MBH = 4*108 M0 Ld = 1046 erg/s fB,order = 0.2 MBH = 5x109 M0 would produce too cold disk -> fails to produce frequency-dependence of polarization. Preliminary Follow-up observations in Aug. 2017 (low state): Very low polarization.

Summary Successful SALT Large Programme for spectroscopy / spectropolarimetry follow-up of transients 7 flaring blazars followed-up in 2016/2017 Spectropolarimetry allows one to disentangle different radiation components (synchrotron vs. disk vs. SSC) 4C+01.02 (z = 2.1) successfully modelled with synchrotron-dominated optical emission; small disk contribution at the blue end. Constrain BH mass to ~ 4*108 M0 Supported by the South African Research Chairs Initiative (SARChI) of the Department of Science and Technology and the National Research Foundation of South Africa.